The present invention relates to hard disk drives. More particularly, the present invention relates to methods and apparatus for preventing damage to the components of the hard disk drive such as the read/write head, the disk surface, and/or the spindle motor in the event of a microprocessor failure.
Hard disk drives have long been employed for storing data in computer systems. To facilitate discussion, FIG. 1 is a simplified diagram of a hard disk drive 100, representing a hard disk drive known in the art. Hard disk drive 100 includes one or more data storage disks 102, which spins around a spindle by spindle motor 104. A read/write (R/W) head 106 couples to an actuator arm 108, which is urged by a voice coil 110 to move R/W head 106 between the inner diameter (ID) 112 and the outer diameter 114 of disk 102 to access data stored on the surface of disk 102. Although only one disk 102 and one actuator arm 108 are shown for simplicity, it should be understood that a typical hard disk drive may include multiple disks stacked in a spaced apart relationship. Each disk may be accessed both at its upper and lower surfaces by actuator arms, which are coupled to an actuator arm assembly comprising multiple actuator arms.
Voice coil 110 is controlled by a microcontroller or microprocessor 114 via a digital-to-analog (DAC) converter 116 and voice control motor (VCM) driver 117, which is shown disposed in a VCM circuit 118, all of which are conventional in construction. It should be noted that the term "microprocessor" is employed herein to also include microcontrollers, or any set of logic circuits capable of performing functions typically expected of a microprocessor. VCM circuit 118 and optionally DAC 116 may be implemented as a single chip, e.g., using a class of devices known as Application Specific Integrated Circuits (ASICs). During operation, microprocessor 114 communicates with a spindle motor driver circuit 120, which controls, among others, the rotation speed of spindle motor 104.
As is well known to those skilled, R/W head 106 does not physically contact the surface of disk 102 when reading data from or writing data to disk 102. More typically, R/W head 106 glides over the surface of disk 102 on a thin layer of air as disk 102 spins. When disk 102 stops spinning, voice coil 110 typically brings R/W head 106 over a designated landing zone on disk 102 to enable R/W head to safely "park." In the example of FIG. 1, the landing zone is shown as concentric landing zone 122, which is adjacent to ID 112 in FIG. 1.
If the power supplied to hard disk drive 100 is uninterrupted and microprocessor 114 has not failed, microprocessor 114 itself can always park R/W head 106 in the landing zone when data access is no longer desired. If power is interrupted, microprocessor 114 would of course be no longer able to perform this parking function. In recognition of this problem, there are provided in the prior art techniques for detecting the power loss condition via an appropriate power monitor circuit, e.g., power monitor circuit 124. Upon detecting a power loss condition, the back EMF (electromotive force) of spindle motor 104 is employed to generate power to a parking circuit 126, which then parks R/W head 106 in the designated landing zone. The use of the back EMF in this manner is well known and is not discussed in detail herein order not to unnecessarily obscure the invention.
While the prior art technique is effective at preventing R/W head 106 from crashing into the media-containing portion on the surface of disk 102 when a power loss condition occurs, there are some disadvantages. For example, it is recognized by the inventor herein that head crashes occur not only upon the occurrence of a power loss condition but may also occur when the microprocessor, e.g., microprocessor 114 fails. In this case, a head crash into the data zone may occur even when there is no power interruption to hard disk drive 100.
More often than not, a microprocessor failure negates the use of the microprocessor as the controlling device for voice coil 110. When this happens microprocessor 114 cannot be counted on to reliably bring, via voice coil 110, actuator arm 108 (and R/W head 106) to the position where safe landing occurs. Since power loss is not detected, power monitor circuit 124 does not issue the command for head park circuit 126 to park R/W 106 in the landing zone. Accordingly, R/W head 106 simply crash lands on the data-containing zone of the surface of disk 102.
For most drives, this crash landing causes damage to the data zone where R/W head 106 impacts. It may be possible, in some instances, for the head to be airborne again when the disk is subsequently started up, and the damage, however unpleasant, is fairly localized.
For some newer drive designs, however, the crash landing of the R/W head on a data zone is nearly always fatal. By way of example, when a type of R/W head known as magneto-resistive head is employed in a drive, the disk surface is typically very smooth to accommodate the low-flying head, e.g., flying at 2 micro-inches above the data-containing disk surface or even lower. It has been found that the smooth mating between the head and the polished disk surface, if such is ever allowed to occur, may give rise to a very high stiction force, i.e., the force existing between the disk surface and the head that resists a subsequent separation.
The stiction force in some disk drive design may be so high that it would be impossible to separate the head from the smooth disk surface after they make contact. In some cases, it is simply impossible to spin up the disk again. In other cases, the drive cannot be started up again without ripping out the head and/or causing severe damage to the disk surface. For these types of drives, therefore, it is necessary to always park the head at a section of the disk surface where safe landing may occur, e.g., where surface texture is introduced to reduce the stiction force.
Additionally, microprocessor failure may cause spurious data to be sent to spindle motor driver circuit 120, which may, in some instances, cause spindle motor 104 to draw an excessive amount of current. Again, since the microprocessor has failed, it cannot be counted on to correct the situation. If too much current is drawn by spindle motor 104, irreversible damage to the motor components may occur.
In view of the foregoing, there are desired improved methods and apparatus for preventing damage to the components of the hard disk drive such as the read/write head, the disk surface, and/or the spindle motor in the event of microprocessor failure and without requiring the intervention of the microprocessor. To minimize costs, the improved methods and apparatus preferably require minimal re-engineering of existing drive designs in their implementation.